The present invention relates to a driving force control for an automotive vehicle.
The term xe2x80x9cstandard running resistancexe2x80x9d is herein used to mean any force, which opposes the motion of an automotive vehicle which is driven to keep on rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. The term xe2x80x9crunning resistancexe2x80x9d is herein used to mean any force that opposes the motion of an automotive vehicle, which is driven to keep on rolling over the surface of a road at a constant vehicle speed. Running resistance is equal to standard resistance if an automotive vehicle is driven to keep on rolling over the surface of a flat road having 0% gradient at a constant vehicle speed. Running resistance increases and becomes greater than standard resistance if the automotive vehicle is accelerated to increase speed from the constant vehicle speed. The term xe2x80x9cacceleration resistancexe2x80x9d is herein used to mean this increment or difference in running resistance that has occurred due to acceleration. Running resistance is greater when the automotive vehicle is driven to keep rolling over the surface of a flat road having gradient greater than 0% at a constant vehicle speed than standard resistance for the same vehicle speed. The term xe2x80x9cgradient resistancexe2x80x9d is used to mean this increment or difference in running resistance.
JP-A 9-242862 discloses a vehicle control system in which a gear ratio of an automatic transmission is selected in response to road gradient, throttle opening degree and vehicle speed. In order to estimate road gradient of a road, over which the vehicle is rolling, a road gradient torque (Txcex1) is determined by subtracting from a driving torque (To) a sum of a flat road running resistance torque (Tr) and an acceleration resistance torque (Txcex1). A characteristic of variation of flat road running resistance torque (Tr) against variation of vehicle speed is mapped. This mapped data are retrieved using a current reading point of vehicle speed to give a value of flat road running resistance torque (Tr).
JP-A10-329585 discloses technique to enhance transient response to a step-like change in target driving force, which occurs when, for example, an accelerator pedal is depressed greatly. The target driving force is defined as required output on vehicle driving axle for keeping the vehicle rolling on the surface of a road having road gradient at a vehicle speed with a depressed position of an accelerator pedal. Thus, the target driving force is determined in response to accelerator depressed position, vehicle speed, and road gradient. A change in the target driving force over an interval between the current and preceding control cycle is determined and used to select an appropriate time series waveform. This waveform gives time series data of variation of target driving force. Engine torque control and a CVT ratio control are carried out to accomplish the target driving force.
JP-A 8-200112 discloses a driving force control system wherein, during traction control, a wheel slip determines a target engine torque and operator depression of an accelerator pedal determines a correction amount. This correction amount is added to the target engine torque to determine a corrected target engine torque. An electronically controlled throttle is controlled to cause the engine to produce the corrected target engine torque.
Each of the above-mentioned known systems is satisfactory to some extent. However, a need remains to provide a driving force control system that can cope with a temporal drop in running resistance. If, with the target driving force kept constant in response to constant operator power demand, such temporal drop in running resistance occurs, the vehicle body may be subjected to shock caused by disturbance owing to this temporal drop in running resistance.
An object of the present invention is to improve a driving force control system of the type wherein an increase in running resistance is used to determine a correction amount in driving force and the determined driving force correction is added to an ordinary target driving force to give a corrected driving force, such that a temporal drop in running resistance may not cause any substantial shocks.
U.S. patent application Ser. No. 09/518,691, filed Mar. 3, 2000 entitled xe2x80x9cDriving Force Control With Gradient Resistance Torque Dependent Correction Factorxe2x80x9d is pending and has been assigned to the same assignee to which the present application is to be assigned. This United States Patent Application claims priority based on Japanese Patent Application No. 11-58289 filed in Japan on Mar. 5, 1999.
This United States Patent Application has proposed a driving force control system that includes an ordinary target driving force generator that generates an ordinary target driving force (tTd#n), and a running resistance increment generator that generates a running resistance increment (RESTRQ). The ordinary target driving force (tTd#n) is given after retrieving a map using accelerator pedal opening (APO) that is equivalent to operator""s depression of the vehicle""s accelerator pedal and vehicle speed (VSP). The proposed driving system further includes a driving force correction generator that determines a driving force correction (ADDFD) in response to the running resistance increment (RESTRQ), and a corrected target driving force generator where the driving force correction (ADDFD) is added to the ordinary target driving force (tTd#n) to produce a corrected target driving force (tTd). This corrected target driving force (tTd) is used to determine a target engine torque (tTe) and a target CVT ratio (tRATIO).
Referring to FIG. 7, let us now assume the case where the automobile travels against actual running resistance that is unaltered. In FIG. 7, at moment t0, a wheel slippage occurs on a manhole cover, and at moment t2, the wheel slippage ceases. This causes a temporal drop between t0 and t2 in actual running resistance increment. In the proposed driving force control system, this temporal drop is reflected in running resistance increment (RESTRQ) after a delay that is unavoidable. Thus, the corresponding temporal drop in running resistance (RESTRQ) begins at moment t1 and terminates at moment t3. In response to this temporal drop in running resistance increment (RESTRQ), the driving force increment (ADDFD) drops for a temporary period t1-t3 as shown by the dotted line in FIG. 7. This temporal drop in driving force increment causes a temporal drop in corrected target driving force (tTe), so that automobile is subjected to an undesired change in acceleration as shown by the dotted line in FIG. 7. This undesired change in acceleration produces shocks.
Accordingly, the present invention aims at improving the driving force control system of the above kind such that occurrence of substantial shocks, which may be induced by a temporal change in running resistance increment, is prevented or at least reduced.
According to one aspect of the present invention, there is provided a driving force control system for an automotive vehicle powertrain including a prime mover and an automatic transmission, the driving force control system comprising:
a first sensor to detect the vehicle""s operator demand on driving force to drive the vehicle;
a second sensor to detect a predetermined parameter indicative of vehicle speed of the vehicle; and
a microprocessor that is programmed to be operative to determine a target value indicative of driving force in response to the vehicle""s operator demand on driving force and the vehicle speed,
to determine a running resistance increment,
to determine a preliminary correction in response to the determined running resistance increment,
to subtract a preceding value of correction from the determined preliminary correction to give a variation,
to limit said variation between upper and lower limits to give a limited variation,
to add the preceding value of correction to the limited variation to give a current value of correction, and
to correct the determined target value with the current value of correction.
According to another aspect of the present invention, there is provided a driving force control system for an automotive vehicle powertrain including a prime mover and an automatic transmission, the driving force control system comprising:
a first sensor to detect the vehicle""s operator demand on driving force to drive the vehicle;
a second sensor to detect a predetermined parameter indicative of vehicle speed of the vehicle
a target value generator to determine a target value indicative of driving force in response to the vehicle""s operator demand on driving force and the vehicle speed;
a running resistance increment generator to determine a running resistance increment that represents an increase in running resistance from a standard running resistance;
a correction generator to determine a correction in response to the running resistance increment;
a corrected target value generator to correct the determined target value with the correction,
said correction generator being operative to calculate a differential, with respect to time, of the correction and operative to tune the calculated differential, and also operative to alter the correction by the tuned differential.
According to still another aspect of the present invention, there is provided a driving force control method for an automotive vehicle powertrain including a prime mover and an automatic transmission, the driving force control method comprising:
detecting the vehicle""s operator demand on driving force to drive the vehicle;
detecting a predetermined parameter indicative of vehicle speed of the vehicle;
determining a target value indicative of driving force in response to the vehicle""s operator demand on driving force and the vehicle speed;
determining a running resistance increment that represents an increase in running resistance from a standard running resistance;
determining a correction in response to the running resistance increment;
correcting the determined target value with the correction;
calculating a differential, with respect to time, of the correction;
limiting the calculated differential to give a limited differential; and
altering the correction by the limited differential.